190 KNOTT AND TANAKADATE 



observer is, thereby producing a possible magnetic disturbance. A 

 specimen slieet is liere reproduced of a single complete experiment 

 for determining the horizontal force. Tlie torsion and arc corrections 

 are apjilird in llic usual way; and the time correction is applied so 

 as to ivduce the time-unit at once to tlie mean solar second. 



As already mentioned, it was found most convenient to take the 

 vibration experiment before the deflection experiment, thereby saving 

 tlie time necessary for the adjustment of the swinging magnet. From 

 the first recorded swing to the last deflectiiw adjustment the whole 

 experiment toDk 23 minutes. * 



The observations of Dip were made in the usual way. Tiie 

 maofnetization of the needle was reversed liv means of the larj^e 

 magnets tliat form an essential part of the apparatus. It might be 

 remarked, however, that, if the electromagnetic declinometer is used, 

 it wouM be much more convenient for the observer to provide himself 

 with a suitable coil f )r revei'sing the magnetization of the dipping 

 needle. The large magnets would not then be recpiired, and the 

 necessity done away with of constantly removing them 15 or 20 yards 

 from the tent whenever a declination experiment was to be made. 

 For, cluscd tlunigh these magnets are, they cause an appreciable 

 disturbance within a distance of a few yards from tlie magnetometer. 



On the occasions on which a series of observations of the dip 



• It is impossible, I believe, to go through these operations witli tlie Kew Instrument so 

 rapidly as tliis. The f:;ain of time with Mr. Tanakadate's instrument seems to be in the 

 deflection experiment, iu wliich the small deflected magnet is much more quickly damped 

 than is possible mth the comjiaiutively large magnet used in the Kew Instrument In 

 my opinion there is quite an unnecessary amount of manipulation required in using tlu; 

 Kew Magnetometer as at present constructed. A small magnet mounted in a manner 

 siuiilar to Mr. Tanakadate's hardly ever requires a renewal of the suspension line», delicate 

 though that is. It requires but to be placed in position, and the deflection experiments 

 begun. A slight modification iu this direction would enable us to dispense with the deflec- 

 tion box altogether, and considerably shorten the time requiri.'d to uiake a deflectiou 

 experiment. [C. O. K.] 



